1. Field of the Invention
The invention, according to the various embodiments described herein, relates to coupling a broadband signal without a galvanic connection.
2. Discussion of the Background
For galvanically separating measurement signals, isolating transformers are well suited. It is though not possible to transform durational current (direct current), DC, through transformers. The relationship of an upper cut-off frequency to a lower cut-off frequency of transformers can reach a factor of 500, if the transformers are connected to resistors on both sides and comprise a highly permeable magnetic core. It is even possible to further increase this factor.
For coupling the complete signal galvanically separated, it is necessary to couple a durational current part of the input signal. This durational current signal part can for example be coupled using optical couplers. The bandwidth which can be reached using such a system is limited by the bandwidth of the optocoupler and of the transformer. For example, if the optocoupler reaches a bandwidth of 500 kHz and the transformer has a relative bandwidth of 500:1, the system can maximally have a bandwidth of 500×500 kHz=250 MHz. This theoretical calculation, though, is very optimistic. In reality, far lower system bandwidths are reached. Moreover, a system using optocouplers and transformers is prone to offset errors. Also, merely a low signal-to-noise ratio is attainable using such systems.
Furthermore, it known from the state of the art to modulate the entire input signal with a rectangle signal with a frequency of at least double the highest frequency component of the input signal. This modulated input signal is then transformed entirely through a single transformer. This isolation coupler, though, comprises several disadvantages. Since it is necessary to modulate the signal with the double frequency than the highest frequency component, a large percentage of the attainable bandwidth of the transformer is wasted. Moreover, if the theoretical bandwidth of the transformer is used to a high degree, production tolerance is a significant factor for the attainable accuracy and signal-to-noise ratio.